Field of the Invention
The invention relates to a device for detecting the presence of particulate material in a fluid stream flowing through a conduit and more particularly to a probe means which is positioned directly in a production flow steam for indicating the presence of particulate material, such as sand, which is being produced along with products from an oil or gas well.
Discussion of the Prior Art
The production of fluid minerals such as oil and gas often involves accompanying particulate material, especially sand. The presence of particulate matter in fluid minerals causes the blockage of flow lines, accumulation in field separators, and damage to production equipment necessitating stoppage of production, cleaning and repair of affected equipment. It has been found that these problems can be circumvented to some extent by controlling the flow rate of produced minerals so that the volume of sand produced is maintained at an acceptable level. See U.S. Pat. No. 3,563,311, issued Feb. 16, 1971.
To maintain the flow of sand in the production of oil or gas at an acceptable level, it is necessary to monitor the production stream from a well. One type of system used to monitor the flow stream to determine wear caused by sand is the erosion probe. This type of probe is inserted directly into the flow stream where the sand will gradually erode the probe wall, at which time the pressure of the flow stream will actuate an alarm indicating that a given amount of erosion has occurred. This type of probe, however, only permits intermitent monitoring of the flow stream.
Another type of probe which permits continuous monitoring of the flow stream is coated with radioactive material. As the sand erodes away the radioactive material, the radiation reading from the probe changes, from which can be calculated the amount of sand flowing through the stream. This type of probe is disclosed in U.S. Pat. No. 3,678,273, issued July 18, 1972.
In the class of acoustical devices for detecting the presence of particulate material, there are devices which can be lowered down into the well during a cessation in production to determine if sand is present in the flow stream. Another type of device which does not require interruption of production is the acoustical flow meter disclosed in U.S. Pat. No. 3,580,092, issued to Scarpa. This acoustical device uses a piezoelectric crystal to detect the presence of particulate material in a conduit. However, this type of device detects the presence of particulate matter in the flow stream; it does not indicate with any precision the actual amount of sand flowing through the conduit.
U.S. Pat. Nos. 3,841,144 and 3,816,773, issued to Baldwin, disclose a means for detecting the presence of particulate matter such as sand in a fluid stream by using an acoustical probe positioned directly in the flow stream. The probe is a hollow cylinder, closed at one end, housing a piezoelectric crystal suspended in oil to acoustically couple the crystal to the housing. Particulate material strikes the housing of the probe which in turn excites the crystal to generate an output signal having a frequency component representative of the particulate material.
The present invention is an improvement over the Baldwin system. The solid probe used in the present invention is easier and cheaper to manufacture than the hollow housing disclosed in the Baldwin patent. Because of its solid construction, it is capable of withstanding greater pressure; it is therefore safer, cheaper to manufacture and more durable than any probe disclosed in the prior art. By locating the transducer external to the probe instead of acoustically suspending it in oil, greater signal response is achieved since the dampening of vibrations by the oil is eliminated.